Light selective element for imaging applications

ABSTRACT

An image sensing device including a package having opposing side portions, an imaging sensor having a top side portion, and a light selective element coupled to the opposing side portions and overlying the top side portion of the imaging sensor.

This application is a Divisional of Ser. No. 09/052,205 filed Mar. 31,1998 now U.S. Pat. No. 6,020,582.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to imaging systems and more particularly topackaging for image sensing devices.

2. Description of Related Art

Image sensing devices generally are characterized as the light detectingcomponent in digital imaging systems. An image sensing device in acamera, for example, uses light to capture an image so as to replacetraditional film-based systems. In a camera, an image sensing device isconfigured to capture a monochrome or color image by way of field effecttransistor (FET) or diode devices, fabricated with complementary metaloxide semiconductor (CMOS) devices or charge couple device (CCD)technology.

Imaging systems built with CCD or CMOS based sensors generally requirean infrared (IR) selective filter as part of the optical system. Thisneed arises because the most common semiconductor-based image sensingdevices, silicon-based image sensing devices respond not only to visiblelight (approximately 380 to 780 nanometers), but also to infrared lightin the range of approximately 780 to 1100 nanometers. Without aninfrared blocking filter, it is virtually impossible to obtain ahigh-quality color image due to the combination of visible and IRsignals. Monochrome imagers also require an IR selective filter tocorrectly preserve scene luminance.

Typically, digital imaging systems incorporate an IR filter, typicallyglass or plastic, as part of the optical train, i.e., somewhere in theoptical system apart from the image sensing device and either overlyingthe lens or interposed within other optical elements. The disadvantageof the inclusion of a separate IR selective filter is that it adds anadditional component to the total system count, i.e., piece-part count.The inclusion of an additional component must be accommodated therebyadding additional complexity to the imaging system. Further, dependingon where the IR selective filter is placed, there is a sizeconsideration that directly affects the cost of the imaging system. Thesystem software and signal processing must also be adjusted toaccommodate the color performance characteristics of the IR selectivefilter. Still further, if the IR selective filter is placed, forexample, in front of the lens, the IR selective filter is exposed to theenvironment and therefore presents the risk of damage by theenvironment, such as for example moisture or scratching.

SUMMARY OF THE INVENTION

An image sensing device is disclosed. The image sensing device includesa package having opposing side portions, the package including animaging sensor having a top side portion, and a light selective elementcoupled to the opposing side portions and overlying the top side portionof the imaging sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an image sensing device in accordance with anembodiment of the invention.

FIG. 2 is a planar side view of the structure of FIG. 1 in accordancewith the invention.

FIG. 3 illustrates a second embodiment of an imaging sensing device inaccordance with the invention.

FIG. 4 illustrates an IR light selective element that is a ionicallycolored glass in accordance with an embodiment of the invention.

FIG. 5 illustrates an IR light selective element that is a ionicallycolored glass coated with a chemical stabilizer in accordance with anembodiment of the invention.

FIG. 6 illustrates an IR light selective element that is a glass coatedwith a hard coating in accordance with an embodiment of the invention.

FIG. 7 illustrates an injection-molding device for forming an IR lightselective element in accordance with the invention.

FIG. 8 illustrates a casting method of forming an IR light selectiveelement in accordance with the invention.

FIG. 9 illustrates an imaging system incorporating an image sensingdevice according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

An image sensing device including a package having a light selective(e.g., absorptive or reflective) element or filter integrated into thepackage is disclosed. In one aspect of the invention, the lightselective element is an IR light selective element. In another aspect ofthe invention, the light selective element is either an ionically-coatedglass, a surface-treated glass, or a plastic substrate. In still anotheraspect of the invention, the light selective element is glass coatedwith an IR light selective coating. In a further aspect of theinvention, an imaging system incorporating a sensor package having aglass substrate overlying the top surface of the package is disclosed.These and other aspects are discussed with reference to the figures.

FIG. 1 illustrates a top-perspective view of an image sensing device ofthe invention. FIG. 1 shows an image sensing device 10 made up of apackage 15 having opposing side wall portions and containing an imagingsensor 20 such as an array of light-absorbing pixels. Imaging sensor 20is embedded into and is affixed by its bottom surface to package 15. Thetop surface of image sensor 20 includes a plurality of pixels, forexample, 640 columns by 480 rows of pixels.

FIG. 2 shows a planar side view portion of the image sensing device ofFIG. 1. In one embodiment, package 15 is made up of a durable material,such as for example a plastic material. The durable plastic packageresists expansion and deformation in the presence of extremetemperatures to which image sensing device 10 may be exposed. In thisembodiment, image sensor 20 is affixed to the bottom of package 15 by anepoxy.

The top surface of package 15 is an IR light selective element or filter25. As illustrated in FIGS. 1 and 2, IR light selective element orfilter 25 is affixed directly to the top of the opposing side portionsof package 15 of imaging sensing device 10. In one embodiment, IR lightselective element 25 is affixed to the side portions of package 15 ofimage sensing device 10 by a thermally stable glue or epoxy. In thismanner, IR light selective element or filter 25 is integrated in package15 and integrated in image sensing device 10.

One advantage of the design of the imaging device of the invention isthat it reduces the piece-part count of the total camera system, sincepackage 15 contains the IR filter rather than a system that requires aseparate placement of the element or filter. An integrated system alsoallows a determination and calibration of color performance to be madedirectly at image sensing device 10, since element or filter 25 is partof image sensing device 10. In other words, the optical characteristicsof image sensing device 10 can be encapsulated so as to more greatlycontrol the system light sensing, e.g., color sensing, reproduction, andcapability. This is to be compared with prior art systems that requiredthat the optical characteristics of the image sensing device to bedetermined separately from the optical characteristics of the IR lightinhibiting or selective element or filter, since the element or filterwas not configured immediately adjacent to or integrated with the imagesensing device.

FIG. 3 shows a perspective side view portion of another embodiment ofthe image sensing device of the invention. In this embodiment, imagesensing device 40 includes a package 15, such as a plastic package,housing imaging sensor 20. Overlying and affixed to the top surface ofthe opposing side wall portions of package 15 by, for example, thermallystable glue or epoxy, is a windowed lid 30. In one embodiment, windowedlid 30 is a ceramic lid.

Windowed lid 30 has an opening 35 into image sensing device 40, theopening having dimensions such that only the light capturing componentsof image sensor 20 are exposed through opening 35. Disposed in opening35 and affixed to the inner walls of windowed lid 30, by, for example,thermally stable glue or epoxy, or otherwise integrated into windowedlid 30, is IR light selective element or filter 25. For a similar sizedimage sensing device as illustrated in FIG. 1, the embodimentillustrated in FIG. 3 uses a smaller, i.e., less surface area, IR lightselective substrate or filter.

The advantages of using a windowed lid package such as illustrated inFIG. 3 include a lower system cost since a smaller portion of IR lightselective element may be used. The smaller IR light selective elementreduces the probability of creating an optical flaw or defect in themanufacture of element 25. The windowed lid also reduces expansionproblems introduced by IR light selective element 25, since element 25is smaller, and expansion due to, for example, temperature changes, is,in general, directly related to the size of element 25. Thus, the riskof cracking of IR light selective element 25 due to expansion is reducedwith a smaller element.

In one embodiment, IR light selective element 25 is chemically-doped orionically-colored glass. FIG. 4 schematically illustrates a topperspective view of an ionically-colored light inhibiting element 25. InFIG. 4, element 25 is doped with an ionic colorant 55, such as forexample copper oxide (CuO).

The processes to make IR selective ionically-colored glass are known.These glasses are generally formed by way of a conventional meltingprocess. In one known process, the chemical dopant responsible forcreating the ionic coloration, i.e., a colorant such as for examplecopper oxide (CuO), is combined in a melting process with a componentresponsible for forming a matrix to support the colorant, such asphosphorous pentoxide (P₂O₅), and silicate, borosilicate, or soda-limeglass and other components to form the ionically-colored glass. In oneembodiment, a suitable ionically-colored glass is a CM-500™ glassdistributed by Hoya Optics of Fremont, Calif., made of the followingweight percents: more than 51% P₂O₅, 11-20% aluminum oxide, 1-10%lithium oxide, and 1-10% copper oxide. In another embodiment, a suitableionically-colored glass is BG 39™ distributed by Schott GlassTechnologies of Duryea, Pa., made of boron oxide, barium oxide, sodiumoxide, potassium oxide, calcium oxide, aluminum oxide, arsenic trioxide,lithium oxide, phosphorous oxide, cerium oxide, and copper oxide.

Ionically-colored glass is potentially more susceptible to interactionwith and attack by moisture and other elements than Borosilicate or sodalime glass. This interaction and attack can degrade the surface polishthrough hydrolization and potentially disrupt the adhesion between theglass and the organic material used to seal the glass to the package orlid. One approach to stabilizing the surface of ionically-colored glass,element, or filter is to overcoat the element with silicon dioxide(SiO₂) or other transparent refractory metal oxides, such as titaniumoxide (TiO₂), by conventional sputtering or evaporation. A coating onthe order of, for example, 20-50 Å is sufficient to protect the seal andprevent moisture from penetrating the surface and interacting with thechemical dopants, for example, CuO in the element.

A second approach of protecting the ionically-colored IR selectiveelement from the deleterious effects encountered in the environment,particularly moisture, is to coat the element with a chemicalstabilizer. A useful chemical stabilizer is available in the form ofadhesion promoters that are used in the integrated circuit waferfabrication industry as a method for improving the adhesion ofphotoresist on substrate films. Examples of adhesion promoters includehexamethyldisilizane (HMDS), trimethylsilylacetamide,diethylaminonitrimethylsilane, glycidoxypropyltrimethoxysilane,3-aminopropyltriethoxysilane, andN-(2-aminoethyl)-3-amino-propyltrimethoxysilane.

The adhesion promoter HMDS, for example, is believed to improve organicphotoresist adhesion by chemically reacting on the wafer surface to forma thin monolayer of essentially pure SiO₂. This film bonds effectivelyto the substrate and provides a suitable surface for good resistadhesion. The reaction may be represented as follows:

2[Si_(S)—OH]+(CH₃)₃Si—N(H)—Si(CH₃)₃→2[Si_(S)—O—Si(CH₃)₃]+NH₃

where “Si_(S)” represents a silicon atom resident in the substratesurface.

According to the invention, ionically-colored element such as glass,that has a component of phosphorous, such as glass doped with ioniccolorant CuO, reacts with an adhesion promoter, such as HMDS, to surfacetreat the glass from exposure to environmental effects such as moistureby forming a thin layer, e.g., 20-50 Å, of SiO₂-like material on thesurface of the glass. More specifically, the adhesion promoter materialreacts to form a siloxane bond with the SiO₂ surface, with an organicmoiety turned outwards. FIG. 5 illustrates a schematic, top perspectiveview of IR light selective element 25 consisting of an ionically-coloredglass 65 and coated with a thin chemical stabilizer layer 70. During thecoating process, multiple surfaces of glass 65 are generally exposed andcoated with chemical stabilizer layer 70. It is to be appreciated thatcare may be taken to prevent a surface from being coated with chemicalstabilizer layer 70 if desired.

One advantage to the adhesion promoter approach over sputtering orevaporating to surface treat an ionically-colored element is that it canbe carried out in simple, lower cost equipment. Examples include, butare not limited to, glass chambers at atmospheric pressure with a smallquantity, approximately 30-50 milliliters, of HMDS liquid as a vaporsource, vacuum prime ovens that combine baking (to drive off moisture)with the introduction of HMDS vapor at sub-atmospheric pressure toprovide the surface treatment. An example of the treatment in a vacuumprime oven includes baking the substrate in dry nitrogen (100° C.,760-10 Torr, 15 min.) and exposing the substrate to HMDS vapor in vacuum(100° C., 10 Torr, 2 min.), and then pumping/purging the system with drynitrogen (100° C., 10-760 Torr, 15 min.). The treatment produces a 20-50Å thick chemical stabilizer layer over the surface of the element orfilter.

A second advantage to the adhesion promoter approach is that it iscompatible with high cleanliness processing. Surface treatment withHMDS, for example, produces virtually no added defects. Sputtering andevaporation with SiO₂ or other transparent refractory metal oxiderequires that the equipment be specially designed and carefully operatedand maintained to ensure low-defect surfaces.

For a discussion of adhesion promoter treatments in integrated circuitprocessing, reference is made to Mittal, K. L., “Factors AffectingAdhesion of Lithographic Materials,” Solid State Technology, May 1979,at 88-96, Helbert, J. N. & Saha, N., “Application of Silanes forPromoting Resist Patterning Layer Adhesion in SemiconductorManufacturing,” J. Adhesion Sci. Technd., Vol. 5, No. 10, at 905-25(1991), and Bourtram, M. E., Howard, A. J., Baca, A. G., Shul, R. J., &Rieger, D. J., “A New Method for Promoting Photoresist Adhesion onTungsten Films for Self-Aligned Refractory Grates on GaAs,” J.Electrochem. Soc., Vol. 140, No. 10, at 2998-3000 (October 1993).

It is to be appreciated that the use of an overcoat or chemicalstabilizer to protect ionically-colored filter elements is not limitedto use with filter elements that are integrated in the image sensingdevice package. Instead, an ionically-colored filter element placedelsewhere in the optical train can similarly be coated and protected asdescribed herein.

In another embodiment of an IR light selective element or filter, acoated element is used instead of an ionically-colored element. Manychemicals for use as a coating material for glass elements are known.The majority of conventional coating materials are manufactured usingthe following “inorganic” evaporation chemicals: Titanium dioxide(TiO₂), silicon dioxide (SiO₂), silicon oxide (SiO), magnesium oxide(MgO), and tantalum pentoxide (Ta₂O₅). Coatings manufactured from thesematerials are highly resistant to damage from abrasion, humidity,corrosive chemicals and solvents, and solar radiation when applied underproper process conditions. These conditions typically include highelement or filter temperature, i.e., greater than 200° C., high vacuumfree of residual hydrocarbon gases and water vapor, precision substratepenetration, including glow discharge, and reactive gas enricheddeposition to form hard coatings.

FIG. 6 schematically illustrates a top perspective view of an IR lightselective element 25 coated with hard coating 85. In an image sensingdevice such as described with reference to FIGS. 1-3, it is to beappreciated that the coated portion of the IR selective element orfilter can face either inside or outside the package.

There are a number of methods of forming IR light selective hard coatingelements including, but are not limited to, deposition, evaporation, andlamination. Representative methods are presented below.

One method of forming IR light selective hard coating elements isthrough an electron-beam evaporation process. In the electron-beamevaporation process, the coating chemical is heated to an evaporationtemperature by bombardment with a beam of accelerated electrons. Inaddition to the high degree of control over the evaporation of thecoating chemical, the electron-beam evaporation process provides theability to achieve extremely high evaporation temperatures.

Another method of forming IR light selective hard coating elements ision-assisted deposition (IAD). The IAD process utilizes conventionalhard coating processes wherein conventionally deposited films are coatedover the element, such as glass, and arrive at the element withrelatively low energy (approximately 1 eV). This low energy level isconsidered to be a primary contributor to the formation of columnar,porous crystal structures. The principal function of the IAD process isto bombard the coating material with accelerated ions in an effort todensify the coating. To form the coated element, an element coated withthe appropriate material is placed in a coating chamber where theelement is exposed to an electrically-charged argon or oxygen gasplasma. When energized, a plasma of high energy particles (approximately120 eV) flows at the element. As the accelerated ions collide with thecoating material which has arrived at the element, the coating materialis compacted creating a much denser film structure. Film packingdensities of 95% can be achieved using the IAD process compared to arelatively porous, columnar crystal structure exhibited by conventionaldeposit of the coating material. The packing density constitutes anincrease of approximately 15% over the typical density achieved usingconventional evaporation processes.

Another method of forming coated IR light selective hard coatingelements is through an ion plating process. Ion plating is based uponthe principal of electromagnetic attraction. This principal is utilizedto achieve uniform, up to 100% dense film layers. Instead of using highkinetic energy to pack coating particles as in the IAD process, the ionplating process relies upon the establishment of electromagneticattraction of coating particles to the element, such as glass, to form adense film.

In the ion plating process, a chemically coated element is placed in achamber equipped with a low-voltage, high-current plasma source which isused to direct a high-current argon plasma at an electron-beamevaporation source. Coating particles become positively charged by theplasma at the point of evaporation. The chamber is designed to allow theformation of a negative electrical charge on the element duringprocessing. The electromagnetic attraction induced by the oppositelycharged coating particles and element provide the necessary accelerationto achieve a uniform film with up to 100% film packing density on thesubstrate.

The processes described above for forming IR light selective hard-coatedelements are known in the industry. Reference is made to the processesdeveloped by Corion Corporation, including the STABILIFE™ ion-platingprocess.

It is to be appreciated that the coated element or filter may be made upof a coating of a single material or a series of coatings of the same ordifferent materials depending on the desired light selectivityrequirements. Balzers Thin Films of Golden, Colo. offers severalsuitable IR light selective hard-coated glass elements, includingproducts marketed under the trade names IRB-1™, IRB-2™, IRB-3™, andCal-Flex™.

The hard coating materials and processes discussed above relatedprimarily to “inorganic” chemical coatings (e.g., TiO₂, SiO₂, MgO,Ta₂O₅, etc.). Organic compounds, compounds having organiccharacteristics, or polymers are also contemplated.

The embodiments described above are typically incorporated into or witha glass (e.g., silicon, borosilicate, soda lime, etc.) or glass-likeelement. Another type of IR selective element contemplated by theinvention is a plastic element. In one embodiment, a plastic substrateis made of a plastic colored with dye, such as an organic dye, that isselective to IR light.

There are various methods of making a plastic element selective to IRlight, including dispersing the dye throughout a plastic substrate,casting the dye in the plastic substrate, or coating the dye on aplastic substrate.

Suitable plastic materials that may serve as the plastic element orsubstrate include, but are not limited to, poly (methyl methacrylate),polycarbonates, or polystyrene. The IR selective dyes include, but arenot limited to, dithiolene and phenyldiamine nickel complex types suchas shown in Table 1.

TABLE 1 Examples of IR Selective Dyes for Filter Applications AbsorptionChemical Structure peak, nm l_(max) I Bis(benzene-1,2-dithiolate) nickelcomplex: 890

II. Bis(4-dimethylamino)dithiobenzil) nickel complex: 1070 

III. Bis(dithiobenzil) nickel complex: 860

IV. Phenyldiamine nickel complex: 790

One method of forming an IR light selective plastic element is throughinjection molding. IR dyes of the type contemplated by the invention aretypically supplied in powder form. Thus, the IR dye(s) is/are combinedwith plastic resins that themselves are typically supplied in pelletform. Methods of mixing include two-roll mills or a Banbury mixer. Aftermixing, the combined material is injected through a conventionalinjection molding device such as illustrated in FIG. 8. Injectionmolding device 200 includes a hopper 210 containing the mixed dye andpowder. Hopper 20 feeds the mixed material into injection chamber 240where the material is melted by heating elements 255 and forced byplunger 230 into nozzle 250. Nozzle 250 discharges the mixed materialinto mold 260 to form the plastic element.

Another method of forming an IR selective plastic element is by casting.In this technique, a plastic monomer such as methyl methacrylatemonomer, is cast into a sheet and polymerized as shown in FIG. 9. First,in step 300, a mold is prepared in the desired shape. Next, as shown instep 310, mold 305 is filled with the monomer and sealed and clamped(step 320). To reduce the evaporation of the monomer, the monomer istypically mixed with polymers. In the embodiment contemplated by theinvention, IR selective dyes are mixed with the monomer/polymer beforecasting. Small amounts of initiator, mold release agents, andsurfactants are added to the monomer/polymer/IR dye mixture. Next, thefilled mold is placed in an oven and heated (step 330) for a sufficientperiod of time to effect polymerization (e.g., 10 hours at 85° C.). Mold305 is then cooled and disassembled (step 340). The cast sheet(s) is/arethen annealed and preshrunk (step 350). Finally, the sheet is cooled(step 360) and cut to desired dimensions for lens applications.

A third way of forming the IR selective plastic elements contemplated bythe invention is by dip coating. In this technique, the IR dye is mixedwith a polymer such as poly(methyl methacrylate) or polycarbonate(s). Anelement that may be plastic, glass, or other suitable element, is dippedinto a solvent system and withdrawn slowly at a controlled speed. Thesolvent system can contain one solvent or a mixture of solvents withfast, medium, and slow evaporation rates that provide a smooth and evencoating. In one embodiment, the viscosity of the solvent system is inthe range of 30-100 mPa-sec. The coated element is then heated toapproximately 160° C. in the case of a polycarbonate element and 120° C.in the case of a poly(methyl methacrylate) element for thirty minutes toremove the solvent.

Table 1 illustrates various dyes having different absorption peaks. Inorder to provide the desired IR selectivity spectrum, it may benecessary to mix or combine two or more dyes. An example of aformulation that provides IR selectivity in the range of 650 nanometersto 1,000 nanometers is: 100 parts by weight polycarbonates, 0.2 parts ofbis(dithiobenzil) nickel complex, 0.2 parts of phenyldiamine nickel, and0.1 parts of (4-dimethylamino dithiobenzil) nickel complex for a coatingof 2 mils. For a molding application, a formulation is 100 parts byweight polycarbonates, 0.01 parts of bis(dithiobenzil) nickel complex,0.01 parts of phenyldiamine nickel, and 0.005 parts ofbis(4-dimethylamino dithiobenzil) nickel complex for a thickness of 1millimeter.

The above discussion focused on the inclusion of an IR selective elementor filter for use in an image sensing system, such as a camera. Ingeneral, applications of such image sensing devices will seek to filter(e.g., reflect or absorb) IR light in the range of 780-1100 nanometers.It is to be appreciated that the element or filter can be made selectiveto other wavelengths as warranted by the particular application and thatthe invention should not be limited to elements selective to a specificspectral range. Instead, the principles set forth herein can be appliedto applications involving various selectivity concerns.

The sensing device and its alternatives described above may be used aspart of a digital imaging system 400 shown in FIG. 9. Imaging system 400has an optical system 430 that channels the incident energy being lightin this case to create an optical image on image sensing device 405.Control signal generation logic 418 is provided to generate the resetsignals and wordlines needed to control photocells of the image sensorof image sensing device 405. The output values (sensor signals) may befurther processed in analog form before being fed to ananalog-to-digital A/D conversion unit 410 that in turn feeds digitalprocessing block 414. Analog signal processing, the A/D unit, andportions of the digital processing block may be located on the same dieas the sensor array. The digital processing may include hardwired logicand/or a programmed processor that performs a variety of digitalfunctions, including preparing digital image data based on the sensorsignals for storage or transmission.

Transmission of the image data to an external processing system may beaccomplished using communication interface 424. For instance, as adigital camera, system 400 will contain a communication interface thatimplements a computer peripheral bus standard such as universal serialbus (USB) or IEEE 1394-1995. Imaging system 400 may also contain localstorage 428 of the non-volatile variety, for instance including a solidstate memory such as a removable memory card, a rotating magnetic diskdevice, or other suitable memory device for permanent storage of digitalimage data. The operation of system 400 may be orchestrated by a systemcontroller 422 which may include a conventional microcontrollerresponding to instructions stored as firmware.

In the preceding detailed description, the invention is described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the claims. The specification and drawings are, accordingly, tobe regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A method comprising: capturing light through animaging system including: a package having opposing side portions, animaging sensor within the package, and a light selective element coupledto the package disposed between the imaging sensor and the capturedlight; and generating an image based on the captured light.
 2. Themethod of claim 1, wherein the light selective element filters infraredlight and the capturing light comprises capturing light incident on theimaging system having a wavelength corresponding to other than infraredlight.